Abstract

2155

Based on our previous studies, we believe that injection of syngeneic dendritic cells (DCs) that have been engineered to produce interferon-α (IFN-α) [DC-IFNα] in the brain tumor microenvironment can enhance the activity of therapeutic immunity, particularly in combinational approaches with peripheral vaccines. This “prime-boost” strategy where vaccine-induced, anti-tumor T cells are recruited into, and sustained within the brain tumor sites may yield improved clinical results over single vaccine modality. In the current study, we first examined the efficacy of this combinational approach in established mouse intracranial tumor models. C57Bl/6 mice bearing syngeneic GL261 glioma or MCA205 sarcoma in the brain received peripheral vaccinations with 1 × 106 granulocyte macrophage-colony stimulating factor (GM-CSF) or interleukin (IL)-4 transfected relevant tumors on days 3, 5 and 7following intracranial tumor inoculation. The animals also received DC-IFNα in the brain tumor site on day 4. Long-term (> 80 days) survival was observed in 50% (3 of 6) of GL261 glioma-bearing animals that received IL-4 transfected GL261 vaccine and DC-IFNα; and in 67% (4 of 6) MCA 205 sarcoma-bearing animals that received GM-CSF transfected MCA 205 vaccine and DC-IFNα, while non of control animals survived longer than 40 days. Following in vitro stimulation with the relevant tumor cells. The splenocytes (SPCs) from long-term survivors demonstrated tumor-specific CTL activities, and these CTL lines expressed high levels of tumor necrosis factor -related apoptosis-inducing ligand (TRAIL) and Fas ligand (FasL) on their surface, and their CTL activities were partially abrogated by pretreatment with concanamycin A (inhibitor of perforin), anti-TRAIL or anti-FasL antibodies. In addition, CTL activities were completely abrogated when target tumor cells were transfected with cDNAs encoding either dominant negative of Fas-associated death domain (FADD-DN), dominant negative of caspase-9 (C9-DN) or FADD-like ICE inhibitory protein (FLIP), suggesting critical roles of perforin-granzyme, Fas-FasL and TRAIL pathways. Because IFN-α is known to enhance TRAIL expression on DCs and T-cells, this combinational strategy may promote unique TRAIL mediated CTL activity. To date, very few citations are available in the literature with regard to critical roles of TRAIL in anti-tumor CTLs. While auto-immune encephalitis is mainly mediated by Fas-FasL pathway, cytokine-transfected tumor vaccines may serve an attractive strategy to induce TRAIL mediated, tumor-selective immune responses.